1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a belt body with a reinforcing fabric cover layer adhered to a surface thereof in such a manner that the thickness of the reinforcing fabric cover layer is substantially uniform over the entire extent of the surface to which it is adhered. The invention also contemplates a method of forming such a power transmission belt.
2. Background Art
It is known in the power transmission belt art to adhesively bond a fabric cover layer to the outer surface of the belt to effect reinforcement thereof. This fabric cover layer is commonly employed in V-ribbed belts. It is common in the prior art to preform an endless band of the fabric cover layer as one of the belt components which are sequentially built up on a cylindrical forming drum. Commonly, the ends of the fabric sheet are joined together to define the endless band of cover fabric which surrounds the forming drum.
Different manners of connecting the ends of the fabric cover layer have been utilized in the prior art. By one method, the ends of the cover fabric are overlapped in defining the endless band. This method of connection is desirable because of the ease with which it can be carried out. Generally, little care is exercised in precisely controlling the extent of overlap. The result of this overlap is a double thickness of the cover fabric which thus produces a step in the band on one surface thereof. The existence of the step is particularly a problem in inversion-type belt formation processes carried out on a forming drum. A brief description of such a conventional forming technique appears below to clarify this problem.
A conventional inversion-type belt formation process for a V-ribbed belt is disclosed in Japanese Patent Publication No. 52-17552. In this publication, a cylindrical forming drum is embraced by a cover fabric having its ends overlapped to produce a localized step resulting from a double thickness of the fabric cover layer. A first, relatively thin, rubber sheet is applied over the fabric cover layer. Load-carrying cords are wrapped around the first layer after which a second, thin, rubber layer and thick, compression rubber layer are sequentially laminated thereover. The resulting belt sleeve is then vulcanized after which V-shaped ribs are defined by grinding grooves in the compression rubber layer. The individual belts can then be separated out of the belt sleeve by known cutting techniques.
While the overlapping of the fabric cover layer ends facilitates formation of the endless fabric band, the production of the step, by reason of the double thickness of the fabric cover layer, can compromise the integrity of the belt formed by the above process. More particularly, the load-carrying cords, which are wrapped around the fabric cover layer, bend around the step in the fabric cover layer. Due to the local deformation of the load-carrying cords, the load-carrying cords effectively slacken as they bend around the step. The result is that when a force is applied to the belt in the region of the localized deformation, the belt tends to elongate in that region more readily than it would along the remainder of the belt. This may disrupt the otherwise smooth running of the belt and results in non-uniform power transmission capabilities along the length of the belt.
Further, as a result of the overlap of the ends of the fabric cover layer, the belt may have a non-uniform thickness, i.e. a bulge or localized thickening at the step, which might cause rough system operation.
Heretofore, it has been virtually impossible to eliminate this localized deformation of the load-carrying cords in the vicinity of the overlapped fabric cover layer, which is commonly overlapped on the order of 4-12 mm. Wrapping of the load-carrying cords too tightly to eliminate the bends therein might result in the load-carrying cords coming too close to or actually penetrating the fabric cover layer.
Another known method of fixing the relative positions of the ends of a fabric cover layer eliminates the deformation of the load-carrying cords, however introduces a further problem. By this method, there is no direct connection between the spaced ends of the fabric cover layer. Rather, the underlying rubber layer adheres to the ends of the fabric cover layer and thereby maintains them in a predetermined relative position. The result is that often there is a gap that remains between the butt edges of the fabric cover layer. The gap produces a point of weakening where the fabric cover layer provides no reinforcement to the belt. There is thus the potential for premature belt failure by reason of this interruption in the fabric cover layer.